1. Field of the Invention
This invention relates to an improved process for the preparation of symmetrical dicumyl peroxide or substituted dicumyl peroxides wherein the substituents are inert substituents in the phenyl ring of the t-cumyl group. More particularly, the invention relates to an improvement in the process of preparing symmetrical dicumyl peroxides by reacting a t-cumyl halide with hydrogen peroxide in the presence of an olefin corresponding to the dehydrohalogenated t-cumyl halide and a phenol catalyst.
2. Description of the Prior Art
The preparation of aralkyl and alkyl peroxides is well known in the prior art and can best be summarized under four major methods of preparation.
(1) The acid-catalyzed condensation of a hydroperoxide with an alcohol.
(2) The acid-catalyzed addition of a hydroperoxide to an olefin.
(3) The displacement reaction between an alkali metal salt of a hydroperoxide and an alkyl halide.
(4) The displacement reaction between a hydroperoxide or hydrogen peroxide and an alkyl halide in the presence of an acid acceptor.
The fourth method is the only method relevant to this invention. The other methods and their short-comings in the preparation of cumyl peroxides are thoroughly discussed in U.S. Pat. No. 4,133,835 (Bafford).
Tijssen (U.S. Pat. No. 3,267,066) in Example IV prepared dicumyl peroxide in 66% yield by reacting hydrogen chloride, .alpha.-methylstyrene, and 70% cumene hydroperoxide for 5 hours at 40.degree. C.
Kato et al. (Auslegeschrift No. 2,035,127) published a process for preparing t-cumyl type peroxides by reacting a tertiary hydroperoxide with an aralkyl halide, such as t-cumyl chloride, at 0.degree.-80.degree. C. in the presence of an acid binding agent such as a t-alcohol or an aliphatic olefin. In this process the hydroperoxide reacts with the aralkyl halide to form the peroxide; the HCl generated is taken up by the acid binding agent. There is no regeneration of the t-cumyl chloride.
Bafford (U.S. Pat. No. 4,133,835) disclosed a process which consisted of adding an aliphatic or cycloaliphatic hydroperoxide to an olefin such as a 1-aromatic-1-substituted ethylene and an aralkyl halide corresponding to the hydrohalogenated ethylene under essentially anhydrous conditions in the absence of a free acid, at a temperature below the decomposition temperature of the halide. The main object of his invention was to provide a process for the preparation of certain peroxides, especially acid-sensitive peroxides, by a procedure that does not use a free-acid catalyst. The process is similar to that of Kato's except Bafford uses the 1-aromatic-1-substituted ethylene as the acid binding agent. By doing this, aralkyl halide is regenerated. Consequently, a low concentration of the aralkyl halide in the olefin can be used; the reaction becomes less acid sensitive and the economics are much better.
Kloosterman et al. (Auslegeschrift No. 1,216,305) describe a process for the preparation of dicumyl peroxide and its ring chlorinated derivatives by the reaction of t-cumyl chloride or its ring chlorinated derivatives with an aqueous solution of hydrogen peroxide at 0.degree.-40.degree. C. in the presence of an acid binding medium so that the pH of the reaction mixture stays between -1 and 2.5 on a glass/kalomel electrode. In a stronger acid medium, decomposition exotherms were reported to occur. A mole ratio of t-cumyl chloride to hydrogen peroxide of 1:0.5 to 1:0.8 were used in this system. The anhydrous basic acid binding agents, such as Na.sub.2 CO.sub.3, K.sub.2 CO.sub.3 or NH.sub.3, had to be added portionwise throughout the reaction so that the pH held between -1 and 2.5.
The process of the present invention has economic advantages over the prior art processes that used cumene hydroperoxide. First of all there is a considerable economic advantage in substituting hydrogen peroxide for cumene hydroperoxide. In addition the present process can be run at a lower temperature and much faster than the reactions of the prior art; therefore a much larger amount of dicumyl peroxide can be made in the same equipment in the same period of time. There is very little buildup of cumene hydroperoxide during the reaction and no apparent breakdown into phenol and acetone. In the prior art processes, this is a very serious problem and approximately 40% of the cumene hydroperoxide decomposes into phenol, acetone and other impurities which contaminate the final product. Since there is no cumene hydroperoxide breakdown, the catalytic amount of phenol present is easily removed, regenerated and recycled. The regenerated phenol is not contaminated with cumene hydroperoxide decomposition products. The excess .alpha.-methylstyrene can be stripped off from the dicumyl peroxide and readily recycled.
When cumene hydroperoxide is used, the .alpha.-methylstyrene is contaminated with cumene since the commercial grades of cumene hydroperoxide contain a considerable amount of cumene. The cumene would have to be separated from the .alpha.-methylstyrene before the .alpha.-methylstyrene could be reused. The reaction is much easier to control and the heat generated during the reaction is less than the prior art reactions because there is no cumene hydroperoxide decomposition occurring. Since the bulk of the reaction occurs very readily, the instant process has been adapted to a continuous process.
Kloosterman (Auslegeschrift No. 1,216,305) was the only inventor in the prior art who reacted hydrogen peroxide with a t-cumyl halide. He used a 50% excess of hydrogen peroxide over the t-cumyl halide and he used weak inorganic bases as the acid binding agents. Although the process worked, the procedure is cumbersome, the reaction period is quite long and he does not regenerate his reactive ingredient, the t-cumyl halide. Kloosterman's reactions took 8 hours to complete while we can run our reactions in anywhere from 1/2 hour to 11/2 hours depending on the reaction conditions. Kloosterman required very tight pH control during his reactions. In most cases he added insoluble weak inorganic bases to the reaction mixture to neutralize the HCl generated in the reaction. This made stirring very difficult and built up the volume in the reactor, decreasing the amount of product that can be made in a given reactor volume. In the instant process .alpha.-methylstyrene prevents formation of HCl by regenerating our active ingredient, the t-cumyl chloride. It allows use of a minimal amount of t-cumyl chloride in the reaction and an increase or decrease in the rate of reaction by increasing or decreasing the t-cumyl chloride concentration and/or the phenol concentration. Kloosterman makes no mention of any catalysts for his process. The effect of the phenol catalyst in the instant process is clearly shown in Example IIB where little dicumyl peroxide was formed in the absence of phenol.